There currently exist a variety of methods and devices for passing electrical current across a barrier having significant pressure differences on either side. There is a need for such methods and devices for use with electrical and optical systems which use vessels that maintain pressure differentials between the inside and outside of the vessel. Such systems include many that are used with lasers, charge coupled device (CCD) arrays, and outer space applications which use vacuum cavities, as well as systems with pressurized containers.
Various methods of creating electrical feedthrus for conduction across pressure envelopes include epoxy encapsulation of insulated wires within a metal interface housing, and metal to insulator glass firing of single conductors within an interface housing.
It is a widely recognized problem in the field that, in systems which require electrical feedthrus across pressure differentials, the location and construction of the feedthrus are often the site of leaks which can cause hazards in the operation of the systems. Other disadvantages to the above methods include epoxy thermal limitations, vacuum outgassing, and leakage repair limitations for the epoxy type feedthru.
An example of the current state of the art of electrical feedthrus for connection across a pressure barrier is that of U.S. Pat. No. 4,804,330 to Makowski et al. which discloses a Hermetic, Vacuum and Pressure Tight Electrical Feedthru. Makowski et al. discloses a leak tight electrical feedthru for vessels which may be evacuated or pressurized relative to the outside ambient conditions. The Makowski et al. feedthru comprises: a ceramic circuit ring which circumscribes the walls of a vessel which is either pressurized or evacuated; the walls of the vessel have an inner circumference which extends into the interior of the vessel and an outer circumference which is exterior to the vessel; a first set of electrical contacts distributed about the inner circumference and demountably connecting with an interior set of electrical cables; a second set of electrical contacts distributed about the outer circumference and demountably connecting with an exterior set of electrical cables; a plurality of filaments fixed on the ceramic circuit ring each of which connects one of the first set of contacts with one of the second set of contacts; and a means for hermetically sealing the ceramic circuit ring to the walls of the vessel. The means for hermetically sealing is via firing a ceramic annular seal ring, which covers the plurality of filaments and fits between the walls of the vessel and the ceramic circuit ring. Metal rings are brazed to the resulting fused module, allowing welding to a housing and common mechanical assembly techniques. The ceramic circuit ring is then bolted to pull the wall sections tight against the annular seal.
None of the above methods has proved suitable for certain applications involving pressure extremes such as outer space applications. Thus there is still a need for a better, more easily reparable, more leak tight method or system for passing electrical current across a pressure envelope.